In 0004688 we decided to fix Printf / string_of_float's handling of nan and infinite values by the MSVC runtime. I think it would be good to extend this sanitization principle to Scanf / float_of_string, to give reliable guarantees on the behavior of %F and the new %H format across platforms.

Note that on mingw64, float_of_string works without any patching (but scanf "%F" does not) - this means it works on the old MSVCRT that mingw64 compiles against, but it's then been broken in more recent versions!